A bug in Yahoo's e-commerce services have caused thousands of US shoppers to have their transactions denied on Cyber Monday, the Monday immediately after Thanksgiving that is famous for high e-commerce traffic.

According to Yahoo's Rich Riley, senior vice president of Yahoo's online channel division, the problem occurred on Monday 26 November at 6am PT (GMT-7).

Customers either met with error messages or were unable to complete their transactions. By 1pm the problem has lessened, and by 6pm, "things were back to normal and the performance of our systems was at 100 percent", Riley wrote in the Yodel Anecdotal corporate blog.

Yahoo spokeswoman Kristen Wareham said in an e-mail at the time the problem was "due to heavy holiday traffic on Yahoo-powered merchant stores."

Despite Yahoo's rapid response to the problem, many of Yahoo's 40,000 merchants in the program were furious about a denial of service that limited sales.

One Yahoo customer, "Montpelerin", wrote online "This is the perfect time for Google to introduce a merchant platform -- we could then accept Google Checkout as well ... are you reading this Google (and Yahoo)?"